Crawler

ABSTRACT

Hardened surface layers ( 12 ) and ( 14 ) of a nitride or other compound, which is higher in hardness than dirt or soil, are formed on the inner peripheral surface ( 11 B) of each metal bush ( 11 ) and on the outer peripheral surface ( 13 A) of each connecting pin ( 13 ) which constitute a crawler belt ( 7 ), respectively. In addition, resinous sliding bearings ( 15 ) which are each formed of an ultra-high molecular weight polyethylene-base resin are fitted in transversely spaced positions on the inner periphery of each metal bush ( 11 ) of the crawler belt. The resinous sliding bearing ( 15 ) is provided with a plural number of recessed grooves ( 16 ) on and around its inner periphery as axially extended grooves. Accordingly, part of soil or dirt which intrudes into a gap space between an outer link portion ( 9 ) of a track link and a metal bush ( 11 ) through an annular seal member ( 17 ) is trapped on an inner peripheral surface ( 15 A) of the resinous sliding bearing ( 15 ) in an embedded state, while remainder of the intruding soil is trapped in the recessed grooves ( 16 ).

TECHNICAL FIELD

[0001] This invention relates to a crawler belt suitable for use oncrawler type vehicles, for example, on hydraulic excavators, hydrauliccranes and the like.

BACKGROUND ART

[0002] Generally, crawler belts which are used on crawler type vehiclessuch as hydraulic excavator and the like are largely constituted by rowsof endlessly connected right and left track links each formed with anouter link portion and an inner link portion at longitudinally oppositeends, respectively, bushes located transversely between the right andleft track links in such a way as to connect inner link portions of therespective track links with each other, connecting pins placed in therespective bushes and each having opposite ends thereof coupled with theouter link portions of the track links by fitting engagement therewith,and seal members provided on the outer peripheral side of the connectingpins between an outer link portion of a track link and a bush.

[0003] The prior art crawler belt of this sort is lapped around an idlerwheel and a drive sprocket and rolled on in the forward or backwarddirection between and around the idler wheel and drive sprocket by adrive means such as hydraulic motor or the like to drive a vehicle bodyin a forward or reverse direction.

[0004] In order to prevent intrusion of soil or dust into gap spacesbetween bushes and connecting pins, it has been known in the art toprovide an annular seal member of rubber or the like between an outerlink portion of each track link and a bush (e.g., as disclosed inJapanese Patent Laid-Open No. H7-285472).

[0005] In the case of the prior art crawler belt seal as disclosed inthe above-mentioned Japanese Patent Laid-Open No. H7-285472, a gap spacebetween an outer link portion of a track link and a bush is sealed up bya seal member, thereby preventing dirt or other foreign matter fromgetting between bush and connecting pin.

[0006] However, once dirt gets into contacting surfaces of the sealmember and bush, for example, it can accelerate abrasive wear of thecontacting surfaces of these members to lower the seal effects of theseal member.

[0007] Besides, in such a case, there also arises a problem that,through a seal member, dirt can get into a gap space between a bush anda connecting pin to accelerate abrasive wear to inner peripheralsurfaces of the bush and/or to outer peripheral surfaces of theconnecting pin.

[0008] Further, dirt which has intruded into a gap space between a bushand a connecting pin tends to accumulate in the gap without beingdischarged to the outside, to hinder smooth relative rotations of thebush and connecting pin as well as smooth movements of the crawler belt.

DISCLOSURE OF THE INVENTION

[0009] In view of the above-discussed problems with the prior art, it isan object of the present invention to provide a crawler belt which canprevent soil or other foreign matter from getting into gap spaces orclearances between bushes and connecting pins of the crawler belt fromoutside, preventing abrasive wear of and damages to sliding surfaces ofbushes and connecting pins which would be caused by the intrusion offoreign matter.

[0010] It is another object of the present invention to provide acrawler belt which can prevent accumulation of soil or other foreignmatter in gap spaces or clearances between bushes and connecting pins ofthe crawler belt to ensure smooth relative rotational movements of thebushes and connecting pins over a long period of time.

[0011] In order to solve the above-discussed problems with the priorart, the present invention contemplates to provide a crawler belt of thesort which includes: endlessly connected right and left track links eachformed with an outer link portion and an inner link portion at oppositelongitudinal ends thereof; bushes transversely located between the rightand left track links in such a way as to connect inner link portions ofthe respective track links with each other; connecting pins inserted inthe bushes and having opposite end portions fitted in and connected tothe outer link portions of the respective track links; and seal membersfitted on the circumference of the connecting pins at positions betweenthe outer link portions of the track links and the bushes.

[0012] The crawler belt according to the present invention ischaracterized by the provision of: a sliding bearing receptacle grooveprovided on and around an inner peripheral surface of each bush, andsaid sliding bearing receptacle groove having a diameter larger thansaid inner peripheral surface; a hardened surface layer provided atleast on an inner peripheral surface of the bush or on an outerperipheral surface of the connecting pin to impart higher hardnessthereto; and a resinous sliding bearing formed of a tubular syntheticresin material lower in hardness than the bush and fitted in the slidingbearing receptacle groove of the bush, the resinous sliding bearinghaving a slide surface on the inner peripheral side thereof in slidingcontact with the connecting pin.

[0013] With the arrangements just described, by the resinous slidingbearing which is fitted in the sliding bearing receptacle groove on theinner peripheral surface of the bush, dirt or soil which gets between anouter link portion and a bush through the seal member during a vehiculardriving operation of the machine can be trapped in an embedded state onthe resinous sliding bearing which is lower in hardness than the bush,precluding a problem of soil accumulation on or between sliding surfacesof the bush and connecting pin. Besides, the hardened surface layerwhich is higher in hardness than intruding soil can prevent abrasivewear of the bush or connecting pin and enhance durability of these partseven if small fragments of soil get between them.

[0014] According to a preferred form of the present invention, thesliding bearing receptacle groove is provided at least in right and leftend portions on the inner periphery of the bush, and the resinoussliding bearing is fitted in each one of right and left sliding bearingreceptacle grooves. With the arrangements just described, the resinoussliding bearing can be located in right and left end portions of thebush thereby to prevent soil from entering a gap space or clearancebetween the bush and the connecting pin from outside.

[0015] Further, according to another preferred form of the presentinvention, the resinous sliding bearing is provided with recessedgrooves on the inner peripheral side thereof for trapping thereinforeign matter coming in from outside. Therefore, soil which hasintruded into a gap space between an outer link portion and a bush canbe trapped in the recessed grooves on the inner periphery of the slidingbearing to prevent same from getting between the bush and connectingpin.

[0016] Further, according to still another preferred form of the presentinvention, a plural number of the recessed grooves are provided atintervals around the inner periphery of the resinous sliding bearing andextended in an axial direction. With the arrangement just described, therecessed grooves as axial grooves can be provided at uniformly spacedpositions around the inner periphery of the resinous sliding bearing toefficiently trap soil or other foreign matter which gets into a gapspace between the outer link portion and the bush.

[0017] Further, according to the present invention, the recessed grooveson the resinous sliding bearing are filled with a lubricant oil. Thelubricant oil in the recessed grooves on the resinous sliding bearingcan be supplied, for example, to sliding surfaces between the bush andthe connecting pin as well as to sliding surfaces between the resinoussliding bearing and the connecting pin for the purpose of reducingsliding resistance.

[0018] Furthermore, according to the present invention, an outer endface of the resinous sliding bearing is held in abutting engagement withthe seal member, and the recessed grooves are each opened at one end onthe side of the outer end of the resinous sliding bearing and closed atthe other end. With the arrangements just described, intruding soil canbe trapped into the recessed grooves through the respective open ends,and trapped soil is blocked at the other closed ends of the respectiverecessed grooves to prevent its intrusion into a gap space between thebush and connecting pin.

[0019] Further, according to the present invention, the seal member iscomposed of an outer lip portion fitted in an outer link portion of atrack link, an inner lip portion slidably held in contact with end facesof the bush and the resinous sliding bearing, and a interconnectingbridge portion connected between the outer and inner lip portionssubstantially in the shape of letter “M”.

[0020] With the arrangements just described, when the seal member isfitted in position between an outer link portion of a track link and abush, the outer lip portion can be resiliently abutted against the outerlink portion, while the inner lip portion is resiliently abutted againstend faces of the bush and resinous sliding bearing. Accordingly, a gapspace between the outer link portion and bush can be sealed up by theseal member in good condition.

[0021] Furthermore, according to the present invention, the seal memberis composed of an annular outer seal member fitted in an outer linkportion of a track link and held in abutting engagement with an end faceof a bush, and an annular inner seal member accommodated within theouter seal member and held in abutting engagement with the outer sealmember and the resinous sliding bearing.

[0022] With the arrangements just described, during a vehicular drivingoperation, the outer seal member of the seal member, which is located onthe side of the resinous sliding bearing, is held in abutting engagementwith an end face of the bush, while the inner seal member is held inabutting engagement with the sliding bearing. In this state, a gap spacebetween the outer link portion and bush and a gap space between theouter link portion and sliding bearing can be sealed up in a stablestate by the inner and outer seal members, respectively.

[0023] On the other hand, according to the present invention, theresinous sliding bearing is formed of at least a synthetic resinmaterial selected from an ultra-high molecular weight polyethylene-baseresin, a polyether etherketone-base resin, a polyterafluoroethylene-baseresin and a polyimide-base resin. With this arrangement, the slidingbearing which is formed of an ultra-high molecular weightpolyethylene-base resin, for example, can enjoy higher resistance toabrasive wear and better lubricative characteristics.

[0024] Further, according to the present invention, the hardened surfacelayer is formed of at least a compound selected from borides, nitridesand carbides. In this case, the hardened surface layer can be enhancedin hardness by using a boride compound layer therefor.

[0025] Moreover, according to the present invention, the hardenedsurface layer on the connecting pin is also likely to be formed of atungsten carbide-base layer by thermal spray coating. In this case, thehardened surface layer can be enhanced in hardness similarly describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the accompanying drawings:

[0027]FIG. 1 is an outer view of a hydraulic excavator adopting a firstembodiment of the present invention;

[0028]FIG. 2 is a fragmentary perspective view on an enlarged scale of acrawler belt shown in FIG. 1;

[0029]FIG. 3 is a partly cutaway plan view of the crawler belt, taken inthe direction of arrows III-III in FIG. 2;

[0030]FIG. 4 is a fragmentary sectional view on an enlarged scale ofconnecting intermediate portions between the track links shown in FIG.3;

[0031]FIG. 5 is an enlarged sectional view of major parts including ahardened surface layer, a resinous sliding bearing and so forth in FIG.4;

[0032]FIG. 6 is an enlarged sectional view of the resinous slidingbearing, taken in the direction of arrows VI-VI in FIG. 4;

[0033]FIG. 7 is a sectional view of the resinous sliding bearing, takenin the direction of arrows VII-VII in FIG. 6;

[0034]FIG. 8 is an enlarged sectional view similar to FIG. 5, showing onan enlarged scale major parts in a second embodiment of the presentinvention, including a hardened surface layer of a crawler belt, aresinous sliding bearing and so forth; and

[0035]FIG. 9 is an enlarged sectional view similar to FIG. 5, showing onan enlarged scale major parts in a modification according to the presentinvention, including a hardened surface layer of a crawler belt, aresinous sliding bearing and so forth.

BEST MODE FOR CARRYING OUT THE INVENTION

[0036] Hereafter, the present invention is described more particularlyby way of its preferred embodiments which are applied to a hydraulicexcavator, with reference to the accompanying drawings.

[0037] Shown in FIGS. 1 through 7 is a first embodiment according to thepresent invention. In these figures, indicated at 1 is a lower structureof the hydraulic excavator. The lower structure 1 includes a track frame2 having right and left side frames 2A (only one of which is shown inthe drawings) which are extended in the longitudinal direction of thevehicle, an idler wheel 3 and a drive sprocket 4 which are provided atthe front and rear ends of each side frame 2A of the track frame 2, anda crawler belt 7 which is wrapped around and between the idler wheel 3and drive sprocket 4 as will be described hereinafter.

[0038] Provided on the side frame 2A of the track frame 2 are an upperroller 5 and a plural number of lower rollers 6 to guide the crawlerbelt 7 on the upper and lower sides of the side frame 2A, respectively.

[0039] Indicated at 7 is a crawler belt which is lapped around andbetween the idler wheel 3 and drive sprocket 4. The crawler belt 7 islargely constituted by track links 8, metal bushes 11, connecting pins13, resinous sliding bearings 15, annular seal member 17, and trackshoes 18, which will be described after. The crawler belt 7 isrotationally driven and rolled forward or backward between and aroundthe idler wheel 3 and drive sprocket 4 by the drive sprocket 4 which ismeshing engagement with the bushes 11, which are provided in theconnecting portions of the track links 8 of the crawler belt 7.

[0040] Indicated at 8 are endlessly connected right and left rows oftrack links which are positioned to confront each other in transverselyspaced positions. The track links 8 are each extended in thelongitudinal direction of the crawler belt 7. An outer link portion 9 isformed at one longitudinal end of each track link unit 8. As shown inFIGS. 4 and 5, the outer link portion 9 is provided with a pin receivingbore 9A to receive a connecting pin 13, a seal fitting bore 9B which isformed by concentrically spreading inner peripheral surface of an innerend portion of the pin receiving bore 9A on the side of a metal bush 11to receive an annular seal member 17, which will be described after, andan inner end face 9C which is formed as a stepped wall between the pinreceiving bore 9A and the seal fitting bore 9B at the deep position ofseal fitting bore 9B.

[0041] Further, an inner link portion 10 is formed at the otherlongitudinal end of each unit of the track links 8. A bush receivingbore 10A is formed in the inner link portion 10 to receive therein ametal bush 11 as described below.

[0042] Denoted at 11 are metal bushes which are interposed between theinner link portions 10 of the right and left track links 8. Each one ofthe bushes 11 is formed in a hollow cylindrical shape by the use ofsteel material, for example, such as carbon steel, alloyed tool steel orthe like, and arranged to receive a connecting pin 13 on the innerperipheral side thereof. In order to facilitate generation of a nitrideor nitrides, the steel material for the metal bushes 11 is preferred tobe of the sort which contains at least one of chromium, molybdenum,titanium, zirconia, niobium and boron as its component.

[0043] Opposite end portions of each metal bush 11 are placed in thebush receiving bores 10A of inner link portions 10 of the right and lefttrack links by press-in fitting to connect between the inner linkportions 10. Each one of the metal bushes 11 is provided with end faces11A at the opposite ends which are received and located in the sealfitting bores 9B of an outer link portions 9 in such a way as to opposethe inner end face 9C through a gap space. Further, the metal bushes 11are each provided with an inner peripheral surface 11B and, as will bedescribed in greater detail hereinafter, a hardened surface layer 12 isformed on the inner peripheral surface 11B to serve as a sliding surfaceto be engaged with the connecting pin 13.

[0044] In this instance, sliding bearing receptacle grooves 11C of adiameter larger than the inner peripheral surface 11B of the metal bush11 are formed at the opposite ends of the inner peripheral surface 11Bof the metal bush 11 to receive resinous sliding bearings 15, which willbe described after.

[0045] Indicated at 12 is a hardened surface layer on the side of bush,that is, a hardened surface layer which is provided on the innerperipheral surface 11B of the metal bush 11. This hardened surface layer12 is formed around the entire inner peripheral surface 11B of the metalbush 11 of steel material, and in the form of a layer of a compoundwhich is harder than dirt or soil.

[0046] In this case, the hardened surface layer 12 is formed by anitriding treatment, a boriding treatment or a carburizing treatment ofthe bush surface to produce a nitride, a boride or a carbide thereon. Inthis instance, the hardened surface layer 12 may be arranged to containone of niride, boride and carbide compounds or to contain two or morethan two such compounds in combination. However, in consideration ofresistance to abrasive wear of the hardened surface layer 12, it isdesirable to adopt a nitriding treatment or a boriding treatment informing the hardened surface layer.

[0047] Indicated at 13 are connecting pins which transversely connectthe right and left track links 8. The connecting pins 13 are each formedin a rod-like shape by the use of steel material such as carbon steel,alloyed tool steel or the like. Similarly to the metal bushes 11, theconnecting pins 13 are preferably formed of steel material whichcontains at least chromium, molybdenum, titanium, zirconia, niobium orboron as a component for encouraging generation of a nitride. Further,through the hardened surface layer 14, the outer peripheral surface 13Aof the connecting pin 13 is slidably fitted in the inner peripheral sideof the metal bush 11 and resinous sliding bearing 15, which will bedescribed hereinafter. Moreover, opposite ends of the connecting pin 13are fitted in the pin receiving bores 9A of outer link portions 9 of theright and left rack links by press-in fitting to connect the outer linkportions 9 transversely to each other.

[0048] Denoted at 14 is a hardened surface layer on the side ofconnecting pin, that is, a hardened surface layer which is provided onthe outer peripheral surface 13A of each connecting pin 13. Similarly tothe above-described hardened surface layer 12, this hardened surfacelayer 14 is formed of a compound which is higher in hardness than dirtor soil grains. Also in this case, as the hardened surface layer 14, anitride, a borate and/or a carbide is produced on the surface of theconnecting pin 13 by a nitriding, boriding or carburizing treatment. Informing the hardened surface layer 14, at least one compound can beselected from nitride, borate and carbide. Otherwise, a tungsten carbide(WC) type thermal spray coating film may be formed on and around theouter peripheral surface 13A of the connecting pin 13 by the use of aflame spray coating method such as high speed gas flame spray coating.

[0049] Indicated at 15 are right and left resinous sliding bearingswhich are provided in transversely spaced positions on the innerperiphery of the metal bush 11. As shown in FIGS. 4 and 7, theseresinous sliding bearings 15 are formed in a cylindrical shape by theuse of a synthetic resin material which is lower than the metal bush 11in hardness and at the same time has satisfactory properties inresistance to abrasive wear and slidability.

[0050] More specifically, the resinous sliding bearings 15 are formed ofone synthetic resin material or more than two synthetic resin materialsselected from ultra high molecular weight polyethylene resin, polyetherether ketone resin, polytetrafluoroethylene resin and polyimid resin.

[0051] The resinous sliding bearings 15 are each placed in a slidingbearing receptacle groove 11C of the metal bush 11 by press-in fitting,and the inner peripheral surface 15A of each resinous sliding bearing 15provides a sliding surface for the connecting pin 13. Further, eachresinous sliding bearing 15 has an outer end face 15B which is locatedat and substantially flush with an end face 11A either at right or leftopen ends of the metal bush 11 for abutting engagement with an annularseal member 17. Provided at the inner end of the resinous slidingbearing 15, away from the outer end face 15B, is an inner end face 15Cwhich is abutted against an inner end of the sliding bearing receptaclegroove 11C.

[0052] Indicated at 16 are a plural number of channel-like recessedgrooves which are provided axially on the inner periphery of eachresinous sliding bearing 15 at angularly spaced positions in thecircumferential direction. As shown in FIGS. 5 to 7, the recessedgrooves 16 are in the form of channel of semi-circular shape incross-section and extended in the transverse direction (in the axialdirection) along the inner periphery of the resinous sliding bearing 15as axial grooves.

[0053] In this instance, one end of each recessed grooves 16 is openedto the outer end face 15B of the resinous sliding bearing 15 as an openend 16A while the other end on the side of the inner end face 15C of theresinous sliding bearing 15 is closed as a closed end 16B. Theserecessed grooves 16 are provided to trap in soil or other foreign matterwhich might intrude into a gap space or interstice between theconnecting pin 13 and the resinous sliding bearing 15.

[0054] Further, the recessed grooves 16 are arranged to function also asan oil reservoir for pooling grease or a lubricant oil therein,maintaining a lubricated state between the metal bush 11 and theconnecting pin 13 and between the resinous sliding bearing 15 and theconnecting pin 13.

[0055] Indicated at 17 are right and left annular seal members which areprovided on the outer periphery of the connecting pin 13 between anouter link portion 9 of each track link 8 and an opposing end of themetal bush 11. The annular seal members 17 are each constituted by aseal ring of M-shape in cross-section, which is formed of a resilientmaterial, for example, a resilient material such as urethane rubber,nitrile rubber or the like.

[0056] In this instance, each annular seal member 17 is constituted byan annular outer lip portion 17A which is fitted in the seal fittingbore 9B of the outer link portion 9, an annular inner lip portion 17Bwhich is slidably abutted against end faces 11A and 15B of the metalbush 11 and the resinous sliding bearing 15, and an interconnectingbridge portion 17C of V-shape in cross-section which is bridged betweenthe outer and inner lip portions 17A and 17B to interconnect sameintegrally with each other.

[0057] Further, the outer lip portion 17A of the annular seal member 17is fitted into the seal fitting bore 9B of the outer link portion 9 asfar as an inner end face 9C of the latter, and abutted against the innerend face 9C with a certain range of compressive resilience. On the otherhand, the inner lip portion 17B on the side of bush is held in contactwith the end faces 11A of the metal bush 11 and the outer end face 15Bof the resinous sliding bearing 15 with a predetermined range ofcompressive resilience. The annular seal member 17 functions to blockintrusion of soil or other foreign matter into a gap space or intersticebetween the connecting pin 13 and the resinous sliding bearing 15, andat the same time to prevent leakage of grease from the recessed grooves16 to the outside.

[0058] Denoted at 18 are track shoes which are made of metal plates andprovided on the right and left track links 8. As shown in FIGS. 2 and 3,the respective tack shoes 18 are securely fixed to the outer side of thetrack links 8 by means of a plural number of bolts 19 or the like toconnect the right and left track links 8 integrally to each other and toform treading surfaces for the crawler belt 7.

[0059] Further, indicated at 20 is an upper structure which is rotatablymounted on the lower structure 1, and at 21 is a working mechanism whichis provided on a front portion of the upper structure 20 for lifting aworking attachment up and down.

[0060] In operation of the hydraulic excavator with the above-describedarrangements according to the present embodiment, each crawler 7 isrolled on in the forward or reverse direction between and around theidler wheels 3 and drive sprockets 4 upon rotationally driving the drivesprocket 4 from a hydraulic motor or the like (not shown) to put thevehicle body in travel in the forward or reverse direction.

[0061] While the crawler belts 7 are being put in rolling movements inthe manner as described above, gap spaces or clearances between theouter link portions 9 of the track links 8 and the metal bushes 11 aresealed up by the respective annular seal members 17 thereby to blocksoil or other foreign matter which might otherwise get between the metalbushes 11 and the connecting pins 13.

[0062] The annular seal members 17 which are formed of a resilientsynthetic resin material undergo deteriorations during use over a longperiod of time, particularly deteriorations in resilient force. Inaddition, in some cases, it becomes necessary to drive the hydraulicexcavator itself by way of the crawler belts 7 for transferring samefrom a working site to a garage or other manageable place. In such acase, irregular loads can be exerted on the annular seal members 17between the track links 8 and the metal bushes 11 to an unexpecteddegree to accelerate deteriorations of their seal capacity or strength.

[0063] With deteriorations in seal capacity or strength of the annularseal members 17, it becomes more likely for soil or dirt to get betweenthe outer link portions 9 and the metal bushes 11 through the annularseal members 17 while the hydraulic excavator is running as a vehicle.Especially when the excavator is driven on a muddy surface, it is verylikely that mud gets between the outer link portions 9 and the metalbushes 11.

[0064] However, according to the present embodiment, resinous slidingbearings 15 which are lower in hardness than the metal bushes 11 areprovided on and around the inner periphery of the metal bushes 11.Therefore, should soil or mud get between the outer link portions 9 andthe metal bushes 11 through the annular seal members 17, part ofintruding soil or mud is trapped in the inner peripheral surface 15A ofthe resinous sliding bearing 15 to block soil which would otherwise tendto intrude between the sliding surfaces of the metal bush 11 and theconnecting pins 13.

[0065] Besides, according to the present embodiment, a plural number ofrecessed grooves 16 are provided at angularly spaced positions aroundthe inner periphery of the resinous sliding bearing 15. Each one of therecessed-grooves 16 is open at one end 16A and closed at the other end16B, and the open end 16A is located face to face with an annular sealmember 17.

[0066] Therefore, a major part of soil which comes in toward a gap spaceor clearance between the connecting pin 13 and the resinous slidingbearing 15 can be effectively trapped into the recessed grooves 16through its respective open end 16A to prevent the soil from gettingbetween the metal bush 11 and the connecting pin 13. In addition,abraded particles which may occur on sliding surfaces of the connectingpin 13 and the resinous sliding bearing 15 can also be trapped in therecessed grooves 16.

[0067] Further, according to the present embodiment, the hardenedsurface layers 12 and 14 of a compound such as nitride, boride orcarbide, which is higher in hardness than the soil, are provided on theinner peripheral surface 11B of the metal bush 11 and on the outerperipheral surface 13A of the connecting pin 13, respectively.Therefore, should soil get between sliding surfaces of the metal bush 11and the connecting pin 13 through the resinous sliding bearing 15, soilgrains can be crushed between the hardened surface layers 12 and 14 toprevent abrasive wear of the metal bush 11 and the connecting pin 13.Besides, crushed soil can be removed from the hardened surface layers 12and 14 and stored in the recessed grooves 16 by letting same escape fromthe hardened surface layers 12 and 14 into the recessed grooves 16through a clearance between the connecting pin 13 and the resinoussliding bearing 15.

[0068] Thus, according to the present embodiment, the resinous slidingbearing 15 contributes to solve the problem of soil accumulation whichwould otherwise occur between the metal bush 11 and the connecting pin13, while maintaining the slide resistance between the metal bush 11 andthe connecting pin 13 at a low level to ensure smooth turning movementsof the crawler belts 7 over an extended period of time.

[0069] Further, since grease or a lubricant is filled in the recessedgrooves 16 on the resinous sliding bearings 15 as describedhereinbefore, sliding resistance between the metal bush 11 and theconnecting pin 13 as well as sliding resistance between the resinoussliding bearing 15 and the connecting pin 13 can be maintained at alowered level by lubrication to guarantee smooth and stable turningmovements of the crawler belt 7 even in an initial stage of a vehiculardriving operation.

[0070] On the other hand, in the case of the present embodiment of theinvention, the hardened surface layer 12 on the side of bush and thehardened surface layer 14 on the side of connecting pin are formed ofthe same compound. Therefore, generally speaking, the two hardenedsurface layers 12 and 14 are considered to be more susceptible tocohesion.

[0071] However, according to the present embodiment of the invention,the resinous sliding bearing 15 of a different constituent in comparisonwith the hardened surface layer 14, is provided on the inner peripheryof the metal bush 11 separately from the hardened surface layer 12 andheld in sliding contact with the connecting pin 13, and grease or alubricant is supplied to a gap space or clearance between the hardenedsurface layers 12 and 14 from the recessed grooves 16 on the resinoussliding bearing 15 as described hereinbefore.

[0072] Therefore, the provision of the resinous sliding bearing 15 witha grease supply contributes to prevent cohesion and scratching bruiseswhich might otherwise occur to the hardened surface layers 12 and 14 andto suppress abnormal metallic noises which would otherwise be producedby the metal bush 11 and the connecting pin 13. Alternatively, cohesionof the hardened surface layers 12 and 14 can be prevented moreeffectively by employing different composition ratios for the hardenedsurface layers 12 and 14.

[0073] Furthermore, the provision of the resinous sliding bearing 15 onthe inner periphery of the metal bush 11 functions to absorb flexuraldeformations of the metal bush 11 which take place when a load isexerted thereon from the side of the drive sprocket 4 during a vehiculartraveling operation, thus suppressing deformations of the connecting pin13 and as a result enhancing durability of the latter.

[0074] Moreover, the provision of the hardened surface layers 12 and 14on the inner peripheral surface 11B of the metal bush 11 and on theouter peripheral surface 13A of the connecting pin 13 function tosuppress flexural deformations of the metal bush 11 and the resinoussliding bearing 15 to a minimum when a load is exerted on the metal bush11 as mentioned hereinbefore.

[0075] On the other hand, each one of the annular seal members 17 isconstituted by the outer lip portion 17A on the side of track link, theinner lip portion 17B on the side of metal bush, and the interconnectingbridge portion 17C which is arranged to interconnect the outer and innerlip portions 17A and 17B in the shape of letter “M”. Therefore, theinterconnecting bridge portion 17C is capable of resilient deformationsbetween the outer lip portion 17A on the side of track link and theinner lip portion 17B on the side of metal bush.

[0076] Consequently, the outer lip portion 17A of the annular sealmember 17 can be resiliently abutted against the inner end face 9C ofthe outer link portion 9 while the inner lip portion 17B on the side ofbush is resiliently abutted against the end face 11A of the metal bush11 and the end face 15B of the resinous sliding bearing 15, to seal upgap spaces or clearances between the outer link portion 9 and the metalbush 11 in a reliable manner. The annular seal member 17 of the abovearrangements can block soil or other foreign matter which tends to getinto a gap space between the connecting pin 13 and the resinous slidingbearing 15 from outside and can prevent grease in the recessed grooves16 from leaking to the outside.

[0077] Turning now to FIG. 8, there is shown a second embodiment of thepresent invention, which has features in that a double layer seal isemployed as a crawler belt seal, including an outer seal member which isfitted in a seal fitting bore of an outer link portion and an inner sealmember which is fitted into a resinous bush from outer side, the outerand inner seal members being put in sliding movements relative to eachother during vehicular driving operations of a machine.

[0078] In the following description of the second embodiment, thosecomponent parts which are common or identical with counterparts in theforegoing first embodiment are designated by common or same referencenumerals to avoid repetitions of same explanations. By the way, in thecase of the following second embodiment, bush receiving bores 10A′ whichare provided in inner link portions 10 of track links 8 are slightlysmaller in diameter as compared with the bush receiving bores 10A in theforegoing first embodiment.

[0079] Indicated at 31 are metal bushes which are employed in thisembodiment of the invention. Similarly to the metal bushes 11 of thefirst embodiment, each one of the metal bushes 31 includes an end face31A, an inner peripheral surface 31B and right and left sliding bearingreceptacle grooves 31C (only one of which is shown in the drawing).Further, the metal bush 31 is placed in a bush receiving groove 10A′ ofan inner link portion 10 by press-in fitting.

[0080] Indicated at 32 are resinous sliding bearings according to thepresent embodiment. The resinous sliding bearings 32 are placed in thesliding bearing receptacle grooves 31C of the metal bush 31. Similarlyto the resinous sliding bearing 15 in the foregoing first embodiment,each one of the resinous sliding bearings 32 includes an innerperipheral surface 32A, an end face 32B to be abutted against a doublelayer seal 34, and another end face 32C to be abutted against a rootportion of the sliding bearing receptacle groove 31C. Further, a pluralnumber of recessed grooves 33 (only one of which is shown in thedrawing) are provided on the inner periphery of the resinous slidingbearing 32. Each one of the recessed grooves 33 is provided with theopen end 33A on the side of the end face 32B and the closed end 33B onthe side of the end face 32C.

[0081] However, the resinous sliding bearings 32 of this embodimentdiffers from the counterpart in the first embodiment in that its outerend face 32B is projected from the end face 31A of the metal bush 31 inthe transverse direction of the crawler belt, and fitted in the sealfitting bore 9B of the outer link portion 9.

[0082] Indicated at 34 is a right and left double layer seal as a sealmember(only one of which is shown in the drawing) according to thepresent embodiment, which are interposed between the outer link portions9 of track links 8 and metal bushes 11. Each one of the double layerseal 34 is constituted by an outer seal member 35 which is fitted on acircumferential portion of the connecting pin 13 within the seal fittingbore 9B of an outer link portion 9, and an inner seal member 36 which islocated within the outer seal member 35 and fitted on a circumferentialportion of the resinous sliding bearing 32 in the proximity to the outerend face 32B of the latter.

[0083] In this instance, the outer seal member 35 of the double layerseal 34 is an annular seal which is formed in an inverted U-shape incross-section by the use of a synthetic resin material, for example, bythe use of urethane rubber or the like. Further, the outer seal member35 is constituted by a first annular portion 35A which is abuttedagainst an inner end face 9C of the outer link portion 9, a tubular bodyportion 35B which is connected angularly to the first annular portion35A substantially in L-shape and fitted in the seal-fitting bore 9B ofthe outer link portion 9, a second annular portion 35C which isangularly connected to the tubular body portion 35B substantially inL-shape and placed at the outer periphery side of the resinous slidingbearing 32 and slidably abutted against the end face 31A of a metal bush31, and an inner seal receptacle groove 35D which is defined by theabove-mentioned first and second annular portions 35A and 35C and theinner periphery of the tubular body portion 35B.

[0084] On the other hand, the inner seal member 36 is an annular sealwhich is formed substantially in a L-shape in cross-section by the useof a synthetic resin material, for example, by the use ofpolytetrafluoroethylene or the like, and accommodated in the inner sealreceptacle groove 35D on the inner peripheral side of the outer sealmember 35. Further, the inner seal member 36 is constituted by a firstannular portion 36A which is slidably abutted against the end face 32Bof the resinous sliding bearing 32 and the first annular portion 35A ofthe outer seal member 35, and a second annular portion 36B which isformed integrally with and radially outward of the first annular portion36A and fitted on an outer peripheral portion of the resinous slidingbearing 32 in abutting engagement with the tubular body portion 35B andthe second annular portion 35C of the outer seal member 35.

[0085] During a vehicular traveling operation, the inner seal member 36of the double layer seal 34, which is provided on the side of theresinous sliding bearing 32, is slidable relative to the outer sealmember 35 on the side of the outer link portion 9. In this state, theouter seal member 35 is held in sliding engagement with the end face 31Aof the metal bush 31, while the inner seal member 36 is held in slidingengagement with the resinous sliding bearing 32, thereby sealing up agap or interstice between the outer link portion 9 and the metal bush 31and a gap or an interstice between the outer link portion 9 and theresinous sliding bearing 32 as well.

[0086] Thus, in the case of the present embodiment with the arrangementsas described above, it is possible to produce substantially the sameeffects as the foregoing first embodiment. Especially in the case of thepresent embodiment employing the double layer seal 34 which is composedof the outer seal member 35 and the inner seal member 36, a contactingsurface of the end face 31A of the metal bush 31 with the annularportion 35C of the outer seal member 35 as well as contacting surfacesof the first and second annular portions 35A and 35C and tubular bodyportion 35B with the inner seal member 36 and a contacting surface ofthe inner seal member 36 with the end face 32B of the resinous slidingbearing 32 can be used as seal surfaces. It follows that seal surfacescan be arranged over a longer distance in total and in the fashion of alabyrinth, that is to say, the double layer seal 34 which is improved inseal capacity and yet simple in construction can be formed simply theuse of the outer and inner seal members 35 and 36.

[0087] In the above-described second embodiment of the invention, theinner seal member 36 of the double layer seal 34 is constituted by onepart. However, it is possible to employ a double layer seal 34′ which isshown in FIG. 9 as a modification. More particularly, in this case ofthe double layer seal 34′, an inner seal member 36′ which isaccommodated in an inner seal receptacle groove 35D of an outer sealmember 35 is constituted by two parts, i.e., a first annular portion36A′ and a second annular portion 36B′.

[0088] Further, in the case of the first embodiment, a couple ofresinous sliding bearings 15 are provided in transversely spacedpositions on the inner periphery of the metal bush 11. However, it is tobe understood that the present invention is not limited to thisparticular arrangement. Namely, if desired, the resinous bush may beprovided either in one position or in three transversely spacedpositions on the inner periphery of the metal bush.

[0089] Moreover, in the foregoing embodiment, by way of example thecrawler type vehicle of the present invention has been described as ahydraulic excavator. However, the present invention is not limited tothe particular example shown. For example, the present invention can besimilarly applied to hydraulic cranes or other crawler type vehicles.

INDUSTRIAL APPLICABILITY

[0090] As clear from the foregoing detailed description, the crawlerbelt according to the present invention is provided with a seal memberto seal up a gap space between an outer link portion of a track link anda bush, a hardened surface layer formed at least on an inner peripheralsurface of the bush or on an outer peripheral surface of a connectingpin to impart higher hardness thereto, a tubular resinous slidingbearing formed of a synthetic resin material lower in hardness than thebush and fitted in a sliding bearing receptacle groove on the innerperipheral surface of the bush. Accordingly, should soil or otherforeign matter get between the outer link portion and the bush throughthe seal member, it can be trapped on an inner peripheral surface of thesliding bearing in an embedded state to prevent soil from accumulatingand getting stuck between sliding surfaces of the bush and connectingpin. Thus, it becomes possible to maintain the sliding resistancebetween the bush and connecting pin at a low level and to turn aroundthe crawler belt smoothly over a long period of time. In addition, evenin case soil gets between the bush and connecting pin, the hardenedsurface layer or layers prevents abrasive wear of the bush or connectingpin to guarantee higher durability of the crawler belt.

1. A crawler belt including endlessly connected right and left tracklinks each formed with an outer link portion and an inner link portionat opposite longitudinal ends thereof, bushes transversely locatedbetween said right and left track links in such a way as to connectinner link portions of the respective track links with each other,connecting pins inserted in said bushes and having opposite end portionsfitted in and connected to said outer link portions of the respectivetrack links, and seal members fitted on circumferential surfaces of saidconnecting pins at positions between said outer link portions of saidtrack links and said bushes, characterized in that said crawler beltscomprises: a sliding bearing receptacle groove provided on and around aninner peripheral surface of each bush, and said sliding receptaclegroove having a diameter larger than said inner peripheral surface; ahardened surface layer provided at least on an inner peripheral surfaceof said bush or on an outer peripheral surface of said connecting pin toimpart higher hardness thereto; and a resinous sliding bearing formed ofa tubular synthetic resin material lower in hardness than said bush andfitted in said sliding bearing receptacle groove of said bush, saidresinous sliding bearing having a slide surface on the inner peripheralside thereof in sliding contact with said connecting pin.
 2. A crawlerbelt as defined in claim 1, wherein said sliding bearing receptaclegroove is provided at least in right and left end portions of said bush,and said resinous sliding bearing is fitted in each one of right andleft sliding bearing receptacle grooves.
 3. A crawler belt as defined inclaim 1, wherein said resinous sliding bearing is provided with recessedgrooves on the inner peripheral side thereof for trapping thereonforeign matter coming in from outside.
 4. A crawler belt as defined inclaim 3, wherein a plural number of said recessed grooves are providedat intervals around inner periphery of said resinous sliding bearing andextended in an axial direction.
 5. A crawler belt as defined in claim 3,wherein said recessed grooves on said resinous sliding bearing arefilled with a lubricant oil.
 6. A crawler belt as defined in claim 4,wherein an outer end face of said resinous sliding bearing is held inabutting engagement with said seal member, and said recessed grooves areeach opened at one end on the side of said outer end of said resinoussliding bearing and closed at the other end.
 7. A crawler belt asdefined in claim 1, wherein said seal member is composed of an outer lipportion fitted in an outer link portion of a track link, an inner lipportion slidably held in contact with end faces of said bush and saidresinous sliding bearing, and a interconnecting bridge portion connectedbetween said outer and inner lip portions substantially in the shape ofletter “M”.
 8. A crawler belt as defined in claim 1, wherein said sealmember is composed of an annular outer seal member fitted in an outerlink portion of a track link and held in abutting engagement with an endface of a bush, and an annular inner seal member accommodated withinsaid outer seal member and held in abutting engagement with said outerseal member and said resinous sliding bearing.
 9. A crawler belt asdefined in claim 1, wherein said resinous sliding bearing is formed ofat least a synthetic resin material selected from an ultra-highmolecular weight polyethylene-base resin, a polyether etherketone-baseresin, a polyterafluoroethylene-base resin and a polyimide-base resin.10. A crawler belt as defined in claim 1, wherein said hardened surfacelayer is at least formed of a compound selected from borides, nitridesand carbides.
 11. A crawler belt as defined in claim 1, wherein saidhardened surface layer on said connecting pin is a thermal spray coatinglayer of tungsten carbide.